The systemic mycoses are important human pathogens responsible for severe pulmonary and disseminated infections. An interest in understanding the pathogenesis of pulmonary mycotic infections emanates from observed differences in the host response to these organisms. Very little investigation into the role of the natural infective particles, the conidia, has been reported, and the initiation events in pulmonary infections induced by these agents have not been previous characterized. Our recently developed murine model of conidial induced pulmonary blastomycosis has demonstrated that macrophages are key cells in the initial host-parasite interaction. Therefore, a close appraisal of the physiologic role of alveolar macrophages in the primary interaction with Blastomyces dermatitidis conidia is crucial to our understanding of the resulting infectivity of this organism. The Specific Aims of this proposal are (1) to establish the mechanisms of attachment between conidia and murine alveolar macrophages, focusing on the mannose receptor, beta-glucan receptor, MAC-1 (CR3). and LFA-1; (2) to measure macrophage functions, including production of interleukin-I (IL-1), tumor necrosis factor (TNF), membrane Ia expression and respiratory burst following exposure to conidia: and (3) to determine the fate of conidia phagocytized by alveolar macrophages. In all phases of the proposed studies both virulent and avirulent strains of B. dermatitidis will be compared. The experimental techniques used to evaluate the role of the different macrophage receptors in attachment of conidia to alveolar macrophages are two-fold. The first is competition for binding by either monoclonal antibodies directed at the receptor in question or second; the addition of soluble competitors for binding (i.e.. mannosyl-BSA for the mannose receptor). Macrophage functions following in vitro interaction with conidia will be assessed by either enzyme immunoassay (TNF) or bioassay (soluble IL-1) of macrophage-conidia culture supernatants, or surface expression and membrane IL-1) on macrophage monolayers. The in vitro microbicidal potential of pulmonary macrophages in the presence or absence of cytokines (IFN-gamma and TNF) will be determined either using standard methodology (colony forming units) or inhibition of 3H-leucine incorporation. In summary, the systemic mycoses serve as models of divergent pathogenesis in chronic pulmonary infections. Clearly it is important to acquire a better understanding of the events responsible for the differences in the pathogenesis of these diseases. The role of the natural infective particles (conidia), as opposed to the yeast phase, has not been adequately studied. The results of proposed studies will provide the basis for future molecular and genetic investigations of this important group of human fungal pathogens.